Development and evaluation of sterile triploids and polyploid breeding methodologies for commercial species of Acacia in Vietnam, South Africa and Australia

• CSIRO Forest Biosciences, Australia
• Forest Science Institute of Vietnam, Vietnam
• CSIR Environmentek, South Africa
• Sylvatech Ltd, Australia
• University of Adelaide, Australia

Several species of Australian Acacias have become commercially important in both tropical and temperate regions. These species have gained widespread acceptance due to their high yields, simple silvicultural regimes, prolific seed production and fast growth rates. These traits, however, also carry a level of risk when introduced into exotic environments, that species will reproduce and spread beyond plantations or planned growth to become invasive weeds. The planting of sterile, but high-yielding varieties would overcome this risk. Some forms of acacias are sterile, offering protection against becoming invasive weeds in exotic environments. The sterility comes from manipulating chromosome numbers (ploidy) in search of improved productivity.

Some forms of polyploid such as triploids formed by mating diploid (2n) and tetraploid (4n) parents, are reproductively sterile which confers possible advantages in tree improvement: more harvestable woody biomass may be produced if energy is not invested in maturing fruits and seeds. When genetic modification technology is developed in the future the availability of sterile genotypes is expected to overcome concern about 'genetic pollution' through uncontrolled outcrossing to non-crop trees. During 2001 Shell International Renewables Ltd. donated tetraploid Acacia mangium (Am) plants to the Forest Science Institute of Vietnam and made available associated technical reports to the Australian partners. This offers potential to grow this species as a sterile but high-yielding variety.

The project is developing and assessing the utility of polyploid breeding methods for commercially important Acacia species, to position for production of triploid plants from elite germplasm for operational deployment. This goal will be achieved via activities within six sub-projects, each involving work by partner organisations in two or more countries.

The project is divided into sub-projects:
To optimise the polyploid induction protocols for Acacia mangium, A. auriculiformis, A. mearnsii and A. decurrens using elite diploid germplasm of all target species, as a platform for production of commercial quality triploid clones. Elite seed of the tropical species will be sent to Australia for experimental optimisation of colchicine induction protocols and the production of 4n plants, which will be returned to Vietnam for multiplication and establishment for future breeding. Protocols will be repeated in South Africa on the temperate species seedlots.
To produce tetraploid A. mearnsii and A. decurrens in RSA using the optimised methodology.
To verify the tetraploid status of the Shell A. mangium clones in Vietnam, and the new A. mearnsii and A. decurrens clones in RSA, and compare efficiency and reliability of alternative methodologies for screening seedlots of all species for induced polyploids. The 36 captured Shell clones will be cultured by FSIV to produce active root tips. These will be sent to Australia for chromosome preparation and counting. Molecular fingerprints will be obtained for all clones to verify that they are distinct genotypes. The utility of isozyme analysis for determination of ploidy levels will be checked. Following the cytology we will repeat the Shell flow cytometry to confirm the methodology. All methods will be repeated on the temperate species in South Africa.
Produce in Vietnam triploid plants of A. mangium and A. mangium X A. auriculiformis by controlled crosses between the Shell tetraploid A. mangium and diploid genotypes of A. mangium and A. auriculiformis. In RSA, position for future production of intraspecific triploid plants of A. mearnsii and A. decurrens.
Raise triploid plants of A. mangium/hybrid, and establish field trials in Vietnam, and Australia for determination of biomass production and reproductive sterility.
Prescribe strategies for incorporating polyploid breeding into Acacia improvement programs, and to communicate these to a wider regional audience via a Workshop and publications.